[css-sizing-4] Wording tweak to distinguish assuming sizes for content vs children better.

Author: fantasai

css-sizing-4/Overview.bs

@@ -413,11 +413,14 @@ Overriding Contained Intrinsic Sizes: the 'contain-intrinsic-size' property</h3>
 
 	This property allows elements with [=size containment=] to specify
 	an <dfn export>explicit intrinsic inner size</dfn>,
-	causing the box to size as if it had contents
-	with a combined width and height
+	causing the box to size as if its content
+	totals to a width and height
 	matching the specified [=explicit intrinsic inner size=]
 	(rather than sizing as if it were empty).
- 
+
+	Note: This is not always equivalent
+	to laying out as if the element had one child of the specified [=explicit intrinsic inner size=].
+
 	Note: An element with [=size containment=] is laid out as if it had no contents [[!CSS-CONTAIN-1]],
 	which in many cases this will cause the element to collapse to zero inner height.
 	This can be corrected with an explicit 'height' chosen to show the expected contents,